1. Field of the Invention
This invention relates to a new valve module which is particularly suitable for use in an exercise device. These devices find particular application in the field of muscle development, exercise and rehabilitation. The new valve module is suitable for a variety of these devices.
2. Description of the Prior Art
In designing strength or exercise training equipment, three types of muscle contractions must be considered. These three types include isometric or static contractions, concentric or positive contractions, and eccentric or negative contractions.
Isometric contractions are contractions in which the length of the muscle remains unchanged while the muscle develops tension. These types of contractions occur when a muscle applies a force against an immovable object. A concentric contraction occurs when the muscle shortens as it develops tension and overcomes the resistance. In an eccentric contraction, the external resistance overcomes the active muscle and the muscle lengthens while developing tension.
The devices of the prior art take into account, some or all of these types of muscle contractions. The devices which only take into account some of the foregoing types of contractions, do not make maximum use of the exercise. If a device or apparatus can take into account all three types of contractions, much more increased development of the muscle will occur during a specific exercise.
The equipment on the market today which in fact takes into account all three types of contractions, is extremely cumbersome and expensive. As a result, this equipment is found only at institutions, health clubs, rehabilitation centers and the like. As a result, they do not have wide-spread use by individuals who require a light-weight, inexpensive and portable apparatus which is suitable for home use and also use at training facilities.
A further drawback of the prior art devices is that they do not provide for differing velocities of movement during the exercise. In other words, the exercise is performed at a continuous rate of speed which restricts the ability of the person doing the exercises from achieving maximum benefit from the exercise. In designing strength training equipment, it is an important consideration to consider the strength curve which is defined as the variation in strength that a muscle undergoes through a range of movement. While different systems have incorporated some aspects of variable resistance in the system, most systems have not provided sufficient means to correlate variable resistance with the strength curve.
One such prior art device is illustrated in U.S. Pat. No. 3,822,599 issued on July 9, 1974 to Brentham. This device is based on the concentric contractions of muscles and does not consider all three types of muscle contractions as set out hereinbefore. Another device by the same inventor, as illustrated in U.S. Pat. No. 4,066,259 granted on Jan. 3, 1978, provides for concentric contractions. Other examples of prior art devices are those available from Keiser which use an air compressor to provide resistance to the exercise movement. The devices require a power source, commonly an electrical power source to run the compressor and thus, are quite limited in use as well as being quite expensive and cumbersome. They also suffer from mechanical breakdown and require a considerable amount of normal servicing.